Arc welding control system and method

ABSTRACT

The present invention provides an arc welding control system and method capable of simultaneously, sophisticatedly performing a weaving width control operation and a torch height control operation. Influence ratios (δ w  and δ z ) of influences of a torch height deviation (ΔP h ) and a groove wall distance deviation (ΔP d ) with respect to a manipulated variable (Δw) of a weaving width and a manipulated variable (Δz) of a torch height are set in accordance with a groove angle (θ) of a workpiece ( 5 ). A calculation unit ( 21 ) calculates the manipulated variables (Δz and Δw) of actuators ( 13  and  14 ) regarding the torch height and the weaving width such that the influence ratios (δ w  and δ z ) become large as the groove angle (θ) becomes large.

TECHNICAL FIELD

The present invention relates to an arc welding control system andmethod of controlling the position of a welding torch in accordance withan arc current or voltage.

BACKGROUND ART

Known is a technology of performing arc welding with respect to aworkpiece that is a welding target while causing a welding torch toautomatically track a weld line of the workpiece. Such an automatic arcwelding device needs to perform a control operation in which whilecausing the welding torch to move in a cyclic manner in a widthdirection of a groove of the workpiece with a specified weaving widthand a specified torch height, the welding torch is caused to move suchthat beads are obtained in a direction along the weld line of theworkpiece. In this control operation, it is necessary to understand arelative positional relation between the welding torch and the weld lineof the workpiece. For example, a position sensor, such as a lasersensor, may be provided on the welding torch. However, the positionsensor is expensive, and in the case of welding a narrow portion, theposition sensor may become an obstacle.

Here, in a welding operation taking advantage of the characteristics ofwelding arc and using an arc sensor that does not require an additionaldevice around the welding torch, the position of the welding torch isunderstood by detecting an arc welding current or arc voltage generatedbetween the workpiece and an electrode projecting from a tip end of thewelding torch and calculating a distance between a tip end of theelectrode and the workpiece. Specifically, weld line tracking can becontrolled by comparing welding current values or arc voltage values atboth ends of weaving, and the torch height can be controlled bycomparing the welding current value or arc voltage value in the weavingwith a target value.

Further, also known is a method of controlling the weaving width inorder to realize an appropriate weaving width with respect to a groovewidth of the workpiece (see PTL 1, for example). In this case, a controloperation of increasing or decreasing the weaving width by comparing thewelding current value or arc voltage value at the end portion of theweaving with the target value is performed.

CITATION LIST Patent Literature

-   PTL 1: Japanese Examined Patent Application Publication No. 4-70117

SUMMARY OF INVENTION Technical Problem

In the above method of PTL 1, the weaving width control operation andthe torch height control operation are performed independently. However,the weaving width control operation and the torch height controloperation influence each other. Therefore, the following problems occurwhen optimizing respective control operations.

Each of FIGS. 11A to 11C is a schematic diagram for explaining problemsin a conventional arc sensor weaving width control operation. In thecase of an initial weaving width w₀ and an initial torch height z₀ asshown in FIG. 11A, a control operation of increasing a weaving width wis performed such that a horizontal distance (wall distance) between anend portion of the weaving width w and the workpiece becomes a targetvalue d_(ref), and a control operation of decreasing a torch height z isperformed such that the torch height z becomes a target value z_(ref).In this case, as shown in FIG. 11B, the horizontal distance between theend portion of the weaving width and the workpiece decreases by thedecrease in the torch height. Therefore, the weaving width w becomeslarger than a target weaving width w_(t) at the target torch heightz_(ref). Generally, the weaving width control operation and the torchheight control operation are changed little by little at everypredetermined control cycle. Therefore, regarding the weaving width w,as shown by a broken line in FIG. 11C, it is desirable that the weavingwidth w gradually get close to the target weaving width w_(t) from theinitial weaving width w₀ as the control cycle is repeated. However, inthe above conventional configuration, the control operation ofincreasing the weaving width w is performed although it is actuallynecessary to perform the control operation of decreasing the weavingwidth w such that the initial weaving width w₀ gets close to the targetweaving width w_(t). Therefore, as shown by a solid line in FIG. 11C,the weaving width w changes in a direction opposite to the target value,and it takes time to stabilize the weaving width w at the target value.

As above, in a case where the weaving width control operation and thetorch height control operation are individually, optimally performed,the horizontal distance between the welding torch and the workpiececonsequently gets too close to each other, and this may cause problemsthat weld defects occur, or the welding torch and the workpiece contacteach other. Therefore, in the conventional method, in order to preventthe problems, such as the weld defects, from occurring whileindependently performing the weaving width control operation and thetorch height control operation, gain has to be decreased in each controloperation, so that high-performance control operations cannot beperformed.

Moreover, the weaving width control operation and the torch heightcontrol operation can be alternately performed in accordance with thecycle of the weaving. To be specific, this method can realize that thetorch height control operation is not performed when the weaving widthcontrol operation is performed, and the weaving width control operationis not performed when the torch height control operation is performed.With this, the problems, such as the weld defects, do not occur.However, regarding each control operation, there exists a period inwhich the control operation is not performed. As a result, the gainssubstantially become half, so that the high-performance controloperations cannot be performed.

The present invention was made to solve the above problems, and anobject of the present invention is to provide an arc welding controlsystem and method capable of simultaneously, sophisticatedly performingthe weaving width control operation and the torch height controloperation.

Solution to Problem

An arc welding control system according to the present invention is anarc sensor control system for arc welding for obtaining satisfactorybeads in a groove of a workpiece that is a welding target, the arcsensor control system including: an actuator configured to cause awelding torch to track a weld line of the workpiece by causing thewelding torch to move in a direction of the weld line of the workpieceat a specified torch height while causing the welding torch to move in acyclic manner in a width direction of the groove of the workpiece with aspecified weaving width; a sensor configured to detect a welding currentor an arc voltage; a calculation unit configured to obtain from thewelding current or the arc voltage a value corresponding to a groovewall distance indicating a horizontal distance between the welding torchand the workpiece at a weaving end portion and a value corresponding tothe torch height, calculate a difference between the value correspondingto the groove wall distance and a target value and a difference betweenthe value corresponding to the torch height and a target value,calculate a manipulated variable of the actuator regarding the weavingwidth from a deviation (hereinafter referred to as a “groove walldistance deviation”) of the value corresponding to the groove walldistance from the target value and a deviation (hereinafter referred toas a “torch height deviation”) of the value corresponding to the torchheight from the target value, and calculate a manipulated variable ofthe actuator regarding the torch height from the groove wall distancedeviation and the torch height deviation; and a control unit configuredto control the weaving width and the torch height based on themanipulated variable regarding the weaving width and the manipulatedvariable regarding the torch height, wherein: a ratio (hereinafterreferred to as an influence ratio) of an influence of the groove walldistance deviation with respect to each of the manipulated variable ofthe weaving width and the manipulated variable of the torch height and aratio (hereinafter referred to as an influence ratio) of an influence ofthe torch height deviation with respect to each of the manipulatedvariable of the weaving width and the manipulated variable of the torchheight are set in accordance with a groove angle of the workpiece; andthe influence ratio of the groove wall distance deviation and theinfluence ratio of the torch height deviation are set such that as thegroove angle becomes large, the influence ratio of the torch heightdeviation becomes relatively larger than the influence ratio of thegroove wall distance deviation.

According to the above configuration, when causing the welding torch totrack the weld line, the manipulated variable of the horizontal actuatorregarding the weaving width and the manipulated variable of the verticalactuator regarding the torch height are calculated using both the valuecorresponding to the groove wall distance and the value corresponding tothe torch height, the values being obtained from the welding current orarc voltage detected by the sensor. In addition, the influence ratios(weight coefficients) by which parameters regarding the groove walldistance deviation and the torch height deviation in respectivemanipulated variables are multiplied are set in accordance with thegroove angle of the workpiece. Then, as a result of diligent studies,the present inventors have obtained findings that by realizing a settingin which the influence ratio of the torch height deviation becomesrelatively larger than the influence ratio of the groove wall distancedeviation in each manipulated variable as the groove angle of theworkpiece becomes large, the weaving width and the torch height can bequickly, optimally controlled without decreasing the gain. Therefore,with the above configuration, the weaving width control operation andthe torch height control operation can be simultaneously,sophisticatedly performed.

The manipulated variable may be obtained by multiplying the influenceratio by an adjustment coefficient for adjusting the influence ratio.With this, even if the groove angle stays the same, a more preferablecontrol performance can be realized depending on the shape and use ofthe workpiece.

Further, a manipulated variable Δz of the torch height may berepresented by Formula 1 below, and a manipulated variable Δw of theweaving width may be represented by Formula 2 below,

$\begin{matrix}{{\Delta\; z} = {K_{z}\left( {{- \frac{\Delta\; P_{d}}{t}} + {2\; K_{h}\Delta\; P_{h}}} \right)}} & {{Formula}\mspace{14mu} 1} \\{{\Delta\; w} = {4\;{K_{w}\left( {{{- \Delta}\; P_{d}} + {{tK}_{h}\Delta\; P_{h}}} \right)}}} & {{Formula}\mspace{14mu} 2}\end{matrix}$

where K_(z) denotes a gain of the manipulated variable regarding thetorch height, K_(w) denotes a gain of the manipulated variable regardingthe weaving width, ΔP_(d) denotes the groove wall distance deviation,ΔP_(h) denotes the torch height deviation, t denotes a value representedby “t=tan(θ/2)” where θ denotes the groove angle, and K_(h) denotes theadjustment coefficient.

According to this, since the influence ratio of the torch heightdeviation in the manipulated variable of the torch height becomes largerthan that in the manipulated variable of the weaving width, the controloperation can be performed while more strongly reflecting the torchheight deviation.

The calculation unit may be configured to: calculate an average value ofthe welding current or arc voltage for each of a plurality of sectionsof one weaving cycle, the welding current or arc voltage being detectedby the sensor, the plurality of sections being obtained by dividing oneweaving cycle into a predetermined number; obtain the valuecorresponding to the groove wall distance based on the average value ofone or a plurality of sections corresponding to the weaving end portionamong the plurality of sections; and obtain the value corresponding tothe torch height based on the average value of the welding current orarc voltage of one weaving cycle. As above, by dividing the weldingcurrent or the arc voltage in accordance with the weaving cycle, the arccurrent or voltage at each position of the welding torch can be easilycalculated.

An arc sensor control method according to the present invention is amethod of controlling an arc sensor for arc welding for obtaining beadsin a groove of a workpiece that is a welding target, the methodutilizing: an actuator configured to cause a welding torch to track aweld line of the workpiece by causing the welding torch to move in adirection of the weld line of the workpiece at a specified torch heightwhile causing the welding torch to move in a cyclic manner in a widthdirection of the groove of the workpiece with a specified weaving width;and a sensor configured to detect a welding current or an arc voltage,the method including the steps of: detecting the welding current or thearc voltage; obtaining from the welding current or the arc voltage avalue corresponding to a groove wall distance indicating a horizontaldistance between the welding torch and the workpiece at a weaving endportion and a value corresponding to the torch height to calculate adifference between the value corresponding to the groove wall distanceand a target value and a difference between the value corresponding tothe torch height and a target value; calculating a manipulated variableof the actuator regarding the weaving width from a deviation(hereinafter referred to as a “groove wall distance deviation”) of thevalue corresponding to the groove wall distance from the target valueand a deviation (hereinafter referred to as a “torch height deviation”)of the value corresponding to the torch height from the target value,and calculating a manipulated variable of the actuator regarding thetorch height from the groove wall distance deviation and the torchheight deviation; and controlling the weaving width and the torch heightbased on the manipulated variable regarding the weaving width and themanipulated variable regarding the torch height, wherein: a ratio(hereinafter referred to as an influence ratio) of an influence of thegroove wall distance deviation with respect to each of the manipulatedvariable of the weaving width and the manipulated variable of the torchheight and a ratio (hereinafter referred to as an influence ratio) of aninfluence of the torch height deviation with respect to each of themanipulated variable of the weaving width and the manipulated variableof the torch height are set in accordance with a groove angle of theworkpiece; and the influence ratio of the groove wall distance deviationand the influence ratio of the torch height deviation are set such thatas the groove angle becomes large, the influence ratio of the torchheight deviation becomes relatively larger than the influence ratio ofthe groove wall distance deviation.

According to the above method, when causing the welding torch to trackthe weld line, the manipulated variable of the weaving width and themanipulated variable of the torch height are calculated using both thevalue corresponding to the groove wall distance and the valuecorresponding to the torch height, the values being obtained from thewelding current or arc voltage detected by the sensor. In addition, theinfluence ratios (weight coefficients) by which parameters regarding thegroove wall distance deviation and the torch height deviation inrespective manipulated variables are multiplied are set in accordancewith the groove angle of the workpiece. Then, as a result of diligentstudies, the present inventors have obtained findings that by realizinga setting in which the influence ratio of the torch height deviationbecomes relatively larger than the influence ratio of the groove walldistance deviation in each manipulated variable as the groove angle ofthe workpiece becomes large, the weaving width and the torch height canbe quickly, optimally controlled without decreasing the gain. Therefore,by performing the control operation using the above method, the weavingwidth control operation and the torch height control operation can besimultaneously, sophisticatedly performed.

The above object, other objects, features and advantages of the presentinvention will be made clear by the following detailed explanation ofpreferred embodiments with reference to the attached drawings.

Advantageous Effects of Invention

The present invention is configured as explained above and has an effectof being able to simultaneously, sophisticatedly perform the weavingwidth control operation and the torch height control operation.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing the schematic configuration of an arcwelding control system according to one embodiment of the presentinvention.

FIG. 2 is a diagram showing a geometric model obtained by modeling apositional relation between a welding torch of a welding system shown inFIG. 1 and a workpiece.

FIG. 3 is a block diagram showing a control model of the welding systemshown in FIG. 1.

FIG. 4 is a diagram showing a trajectory of the welding torch of thewelding system shown in FIG. 1 and an arc voltage change correspondingto the trajectory.

FIG. 5A is a schematic diagram conceptually showing a welding torchcontrol operation of the welding system shown in FIG. 1.

FIG. 5B is a schematic diagram conceptually showing the welding torchcontrol operation of the welding system shown in FIG. 1.

FIG. 6A is a side view showing the shape of the workpiece used inExample 1.

FIG. 6B is a perspective view showing the shape of the workpiece used inExample 1.

FIG. 7A is a diagram showing the arc voltage detected in an arc sensorcontrol operation in Example 1.

FIG. 7B is a diagram showing a deviation of a weaving width from atarget value in the arc sensor control operation in Example 1.

FIG. 8A is a diagram showing a horizontal position trajectory of thewelding torch in the arc sensor control operation in Example 1.

FIG. 8B is a diagram showing a vertical position trajectory of thewelding torch in the arc sensor control operation in Example 1.

FIG. 9A is a diagram showing a time change of the weaving width in thearc sensor control operation in Example 2 and Comparative Example.

FIG. 9B is a diagram showing a time change of a horizontal distancebetween a weaving end and the workpiece in the arc sensor controloperation in Example 2 and Comparative Example.

FIG. 10A is a diagram showing a time change of a torch height of aweaving center in the arc sensor control operation in Example 2 andComparative Example.

FIG. 10B is a diagram showing a time change of an average torch heightin the arc sensor control operation in Example 2 and ComparativeExample.

FIG. 11A is a schematic diagram for explaining problems in aconventional arc sensor weaving width control operation.

FIG. 11B is a schematic diagram for explaining problems in theconventional arc sensor weaving width control operation.

FIG. 11C is a schematic diagram for explaining problems in theconventional arc sensor weaving width control operation.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the present invention will be explained inreference to the drawings. In the drawings, the same reference signs areused for the same or corresponding components, and a repetition of thesame explanation is avoided.

FIG. 1 is a block diagram showing the schematic configuration of awelding system to which an arc welding arc sensor control systemaccording to one embodiment of the present invention is applied. Asshown in FIG. 1, the welding system to which the arc welding arc sensorcontrol system of the present embodiment is applied includes: a weldingmanipulator 1; a calculation control unit 2 configured to control thewelding manipulator 1; a welding power source 3 configured to generatean arc at the welding manipulator 1; and a sensor 4 configured to detectan arc welding current and an arc voltage.

The welding manipulator 1 includes a welding torch 11 including a nozzleconfigured to supply a shielding gas to a welded portion. An electrode12 is provided at a tip end (lower end) of the welding torch 11. Anelectric power line extending from the welding power source 3 isconnected to the welding torch 11, and electric power is supplied to thewelding torch 11. The welding manipulator 1 includes a horizontalactuator 13 configured to cause the welding torch 11 to move in ahorizontal axis direction and a vertical actuator 14 configured to causethe welding torch 11 to move in a vertical direction. Each of thehorizontal actuator 13 and the vertical actuator 14 operates based on acontrol signal output from the calculation control unit 2 and causes thewelding torch 11 to move in the horizontal direction or the verticaldirection. This configuration may be configured by a multiple jointrobot including the welding torch 11 at a tip end portion thereof.

A workpiece 5 that is a welding target is placed under the welding torch11. Regarding the workpiece 5, two welded materials are arranged face toface, and a groove 51 is formed at a portion that should be welded.Regarding the groove 51, two welded materials are arranged face to facesuch that respective groove surfaces form a predetermined groove angleθ. Since there is a case that the vicinity of a portion where the weldedmaterials contact each other is a curved surface, the groove angle θdenotes an angle between surfaces respectively extended from the groovesurfaces.

The welding power source 3 is configured such that the electric powerline of the welding power source 3 is also connected to the workpiece 5.A voltage is applied to between the welding torch 11 (the electrode 12of the welding torch 11) and the workpiece 5 by the electric powersupplied from the welding power source 3, and the arc is generatedbetween the electrode 12 projecting from the tip end of the weldingtorch 11 and the workpiece 5. With this, the workpiece 5 is welded, andthe beads are formed. As the sensor 4, a voltage sensor 41 configured todetect the arc voltage between the welding current and the arc voltageis provided between the electric power line extending between thewelding power source 3 and the welding torch 11 and the electric powerline extending between the welding power source 3 and the workpiece 5.Further, in the present embodiment, a current sensor 42 is also providedas the sensor 4 on one of the above electric power lines. The presentembodiment includes both the voltage sensor 41 configured to detect thearc voltage value and the current sensor 42 configured to detect thewelding current value as the sensors 4 each configured to detect thewelding current or the arc voltage. However, the present embodiment mayinclude only one of these sensors. Moreover, each sensor may directly orindirectly detect the welding current or arc voltage between powersupply lines extending from the welding power source 3. Generally,control operations in MIG welding, MAG welding, and CO2 welding areperformed based on the current value, and a control operation in TIGwelding is performed based on the voltage value. Therefore, theconfiguration may be changed or appropriately used depending on the typeof the welding.

The calculation control unit 2 functions as a calculation unit 21configured to: obtain from the arc voltage or welding current whencausing the welding torch to track the weld line, a value correspondingto a groove wall distance indicating a horizontal distance between thewelding torch 11 at the end portion of the weaving and a groove wall ofthe workpiece 5 and a value corresponding to the torch height; calculatea difference between the value corresponding to the groove wall distanceand a target value and a difference between the value corresponding tothe torch height and a target value; calculate a manipulated variableregarding the weaving width of the actuator (to be specific, amanipulated variable of horizontal actuator 13) from a deviation (agroove wall distance deviation) of the value corresponding to the groovewall distance from the target value and a deviation (a torch heightdeviation) of the value corresponding to the torch height from thetarget value; and calculate a manipulated variable regarding the torchheight of the actuator (to be specific, a manipulated variable of thevertical actuator 14) from the groove wall distance deviation and thetorch height deviation. Further, the calculation control unit 2functions as a control unit 22 configured to control the actuators 13and 14 of the welding manipulator 1 based on the manipulated variableregarding the weaving width and the manipulated variable regarding thetorch height. Specifically, the calculation control unit 2 thatfunctions as the control unit 22 of the present embodiment causes thewelding torch 11 to move in a cyclic manner in a width direction of thegroove 51 of the workpiece 5 that is the welding target with a specifiedweaving width and also causes the welding torch 11 to move in adirection along the weld line of the groove 51 of the workpiece 5 at aspecified torch height based on the welding current or arc voltagedetected by the sensor 4, thereby obtaining the beads on the groove 51of the workpiece 5. The calculation control unit 2 may have anyconfiguration as long as it has a processing function. For example, thecalculation control unit 2 may be constituted by a microcontroller, CPU,MPU, PLC (Programmable Logic Controller), logic circuit, or the like.Moreover, the present embodiment explains a case where one calculationcontrol unit 2 functions as both the calculation unit 21 and the controlunit 22. However, the calculation unit 21 and the control unit 22 may beseparately configured as a control unit and a calculation unit.

Hereinafter, specific control modes will be explained. First, thecalculation control unit 2 obtains the value corresponding to the groovewall distance and the value corresponding to the torch height from thewelding current or arc voltage detected by the sensor 4. For thispurpose, in the present embodiment, the horizontal distance between thewelding torch 11 at the end portion of the weaving and the workpiece 5and the average height of the welding torch 11 are calculated from thearc voltage. FIG. 2 is a diagram showing a geometric model obtained bymodeling the positional relation between the welding torch of thewelding system shown in FIG. 1 and the workpiece.

As shown in FIG. 2, a lower end of the groove 51 is an origin, a y-axisextends in the horizontal direction, and a z-axis extends in thevertical direction. In addition, a central coordinate of the weavingwidth w is (y, z), and these are used as control parameters. Inaddition, a horizontal distance between a left end of the weaving widthw and a left wall (left welded material) of the workpiece 5 is denotedby dl, a horizontal distance between a right end of the weaving widthand a right wall (right welded material) of the workpiece 5 is denotedby dr, and an average value of a vertical distance from a weavingposition to the workpiece 5 is an average torch height h.

Here, as a result of diligent studies, the inventors of the presentinvention have expressed the relations among the above parameters asformulas below. To be specific, each of the horizontal distances dl anddr and the average torch height h is set to be expressed by using acertain ratio of the weaving width w and a certain ratio of an actualtorch height z at a weaving center.

$\begin{matrix}{{\begin{bmatrix}{dl} \\{dr} \\h\end{bmatrix} = {\begin{bmatrix}1 & t & {- \frac{1}{2}} \\{- 1} & t & {- \frac{1}{2}} \\0 & 1 & {- \frac{1}{4\; t}}\end{bmatrix}\begin{bmatrix}y \\z \\w\end{bmatrix}}},{t = {\tan\frac{\theta}{2}}}} & {{Formula}\mspace{14mu} 3}\end{matrix}$

Then, the control model using Formula 3 above is applied to the presentembodiment, and the control unit 22 performs control operations based onthe applied control model. FIG. 3 is a block diagram showing the controlmodel of the welding system shown in FIG. 1. According to the blockdiagram of FIG. 3, Formula 3 is expressed as x=Mu, where x denotes anoutput vector, and u denotes an input vector. A manipulated variable Δuat this time is expressed as Δu=K₂M⁻¹K₁(x_(ref)−x), where x_(ref)denotes the target value, and each of K₁ and K₂ denotes the gain.Relational expressions of respective parameters at this time areexpressed as formulas below.

$\begin{matrix}{\begin{bmatrix}{\Delta\; y} \\{\Delta\; z} \\{\Delta\; w}\end{bmatrix} = {\quad{{{\begin{bmatrix}k_{y} & 0 & 0 \\0 & k_{z} & 0 \\0 & 0 & k_{w}\end{bmatrix}\begin{bmatrix}{1/2} & {{- 1}/2} & 0 \\{{{- 1}/2}\; t} & {{{- 1}/2}\; t} & 2 \\{- 2} & {- 2} & {4\; t}\end{bmatrix}}\begin{bmatrix}1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & k_{h}\end{bmatrix}}\begin{bmatrix}{{dl}_{ref} - {dl}} \\{{dr}_{ref} - {dr}} \\{h_{ref} - h}\end{bmatrix}}}} & {{Formula}\mspace{14mu} 4}\end{matrix}$

Formulas below are obtained by developing Formula 4.

$\begin{matrix}{{{\Delta\; y} = {\frac{k_{y}}{2}\left( {{- {dl}} + {dr}} \right)}}{{\Delta\; z} = {\frac{k_{z}}{t}\left\{ {{- \left( {d_{ref} - \frac{{dl} + {dr}}{2}} \right)} + {2\;{{tk}_{h}\left( {h_{ref} - h} \right)}}} \right\}}}{{\Delta\; w} = {4\; k_{w}\left\{ {{- \left( {d_{ref} - \frac{{dl} + {dr}}{2}} \right)} + {{tk}_{h}\left( {h_{ref} - h} \right)}} \right\}}}} & {{Formula}\mspace{14mu} 5}\end{matrix}$

Here, since it is known that a distance d and a voltage V have arelation of a linear expression (d=mV+b, where each of m and b is aconstant), formulas below are obtained by converting Formula 5 using theabove linear expression.

$\begin{matrix}{{{\Delta\; y} = {\frac{K_{y}}{2}\left( {{- V_{dl}} + V_{dr}} \right)}}{{\Delta\; z} = {\frac{K_{z}}{t}\left\{ {{- \left( {V_{dref} - \frac{V_{dl} + V_{dr}}{2}} \right)} + {2\;{{tK}_{h}\left( {V_{href} - V_{h}} \right)}}} \right\}}}{{\Delta\; w} = {4\; K_{w}\left\{ {{- \left( {V_{dref} - \frac{V_{dl} + V_{dr}}{2}} \right)} + {{tK}_{h}\left( {V_{href} - V_{h}} \right)}} \right\}}}} & {{Formula}\mspace{14mu} 6}\end{matrix}$

According to the above, Δy denotes the manipulated variable of the weldline tracking, Δz denotes the manipulated variable of the torch height,and Δw denotes the manipulated variable of the weaving width.

As a result of the derivations of these formulas, the present inventorshave obtained findings that the weaving width w and the torch height zcan be sophisticatedly, optimally controlled without decreasing the gainby realizing a setting in which regarding each of the above manipulatedvariables, a ratio of an influence of the torch height deviation becomesrelatively larger than a ratio of an influence of the groove walldistance deviation as the groove angle θ of the workpiece 5 increasesaccording to Formula 6.

Here, “V_(dref)−(V_(dl)+V_(dr))/2” denotes the groove wall distancedeviation, and “V_(href)−V_(h)” denotes the torch height deviation.Therefore, when the groove wall distance deviation is denoted by ΔP_(d),and the torch height deviation is denoted by ΔP_(h), the manipulatedvariable Δz of the torch height is represented by Formula 7 below, andthe manipulated variable Δw of the weaving width w is represented byFormula 8 below.

$\begin{matrix}{{\Delta\; z} = {K_{z}\left( {{- \frac{\Delta\; P_{d}}{t}} + {2\; K_{h}\Delta\; P_{h}}} \right)}} & {{Formula}\mspace{14mu} 7} \\{{\Delta\; w} = {4\;{K_{w}\left( {{{- \Delta}\; P_{d}} + {{tK}_{h}\Delta\; P_{h}}} \right)}}} & {{Formula}\mspace{14mu} 8}\end{matrix}$

Here, K_(z) denotes a gain of the manipulated variable regarding thetorch height, K_(w) denotes a gain of the manipulated variable regardingthe weaving width, and K_(h) denotes an adjustment coefficient.

Next, a method of detecting V_(dl), V_(dr), and V_(h) that are inputparameters of Formula 6 obtained as above will be explained. FIG. 4 is adiagram showing a weaving trajectory of the welding torch of the weldingsystem shown in FIG. 1 and an arc voltage change corresponding to theweaving trajectory. An upper side of FIG. 4 shows a graph of a torchweaving trajectory, and a lower side of FIG. 4 shows a graph of the arcvoltage change corresponding to the torch weaving trajectory. In thegraph of the torch trajectory, the initial value is set to zero.

In the present embodiment, the calculation unit 21 is configured to:calculate an average value of the arc voltage for each of a plurality ofsections of one weaving cycle, the arc voltage being detected by thesensor 4, the plurality of sections being obtained by dividing oneweaving cycle into a predetermined number; obtain the value (voltagevalue) corresponding to the groove wall distance based on the averagevalue of one or a plurality of sections corresponding to the calculatedweaving end portion among the plurality of sections; and obtain thevalue (voltage value) corresponding to the torch height based on theaverage value of the arc voltage of one weaving cycle. Specifically, asshown in the lower side of FIG. 4, for example, one weaving cycle isdivided into eight equal sections, an average arc voltage value of thesections (in the example of FIG. 4, sections 1 and 2 among eightsections 0 to 7) corresponding to one weaving end portion is used as avoltage V_(dl) at the weaving end portion, an average arc voltage valueof the sections (in the example of FIG. 4, sections 5 and 6 among eightsections 0 to 7) corresponding to the other weaving end portion is usedas a voltage V_(dr) at the weaving end portion, and an average arcvoltage value of one weaving cycle is used as a voltage V_(h) indicatingthe torch height.

As above, by dividing the welding current or the arc voltage inaccordance with the weaving cycle, the arc voltage at each position ofthe welding torch can be easily calculated. In the present embodiment,the arc voltage at the weaving end portion is detected by dividing oneweaving cycle into eight equal sections. However, the number of dividedsections may be increased or decreased as long as the arc voltage at theweaving end portion can be detected. Moreover, a peak voltage value atthe weaving end portion may be used as the arc voltage at the weavingend portion. Moreover, a voltage at a weaving middle position may bedetected as a voltage indicating a voltage of the torch height. Further,in consumable electrode welding, such as the MIG welding, the MAGwelding, and the CO2 welding, if the distance between a point end of awire that is the electrode 12 and the workpiece becomes equal to orshorter than a predetermined distance, the arc extinction occurs. Thus,the amount of time of short circuit (short circuit duration) increases,and the number of times of short circuit (short circuit frequency)increases. Therefore, the distance between the point end of the wire andthe workpiece can also be estimated by measuring the short circuitduration or the short circuit frequency.

In the present embodiment, the value corresponding to the groove walldistance and the value corresponding to the torch height are obtained bydetecting the arc voltages in the predetermined sections, and thevoltage value itself is compared with the target value (voltage value).However, the present embodiment may be such that the groove walldistance and the torch height are actually calculated from the detectedarc voltage or welding current, and the groove wall distance and thetorch height are compared with corresponding target values (distancevalues).

As above, in the present embodiment, a ratio (hereinafter referred to asan “influence ratio”) of an influence of the groove wall distancedeviation ΔP_(d) with respect to each of the manipulated variable Δz ofthe torch height and the manipulated variable Δw of the weaving widthand a ratio (hereinafter referred to as an “influence ratio”) of aninfluence of the torch height deviation ΔP_(h) with respect to each ofthe manipulated variable Δz of the torch height and the manipulatedvariable Δw of the weaving width are set in accordance with the grooveangle θ of the workpiece 5. Specifically, each of these influence ratiosdenotes an absolute value of a coefficient indicating a weight of thegroove wall distance deviation ΔP_(d) in Formulas 7 and 8 or the torchheight deviation ΔP_(h) in Formulas 7 and 8. The influence ratio of thegroove wall distance deviation ΔP_(d) in the manipulated variable Δw ofthe weaving width is represented by “δ_(wd)=4”, the influence ratio ofthe torch height deviation ΔP_(h) in the manipulated variable Δw of theweaving width is represented by “δ_(wh)=8tK_(h)”, and a ratio(ΔP_(h)/ΔP_(d)) is represented by “δ_(w)=2tK_(h)”. The influence ratioof the groove wall distance deviation ΔP_(d) in the manipulated variableΔz of the torch height is represented by “δ_(zd)=1/t”, the influenceratio of the torch height deviation ΔP_(h) in the manipulated variableΔz of the torch height is represented by “δ_(zh)=K_(h)”, and a ratio(ΔP_(h)/ΔP_(d)) is represented by “δ_(z)=tK_(h)”. As a result, thecalculation unit 21 calculates the manipulated variable Δz of the torchheight and the manipulated variable Δw of the weaving width such thatthe influence ratios δ_(wh) and δ_(zh) of the torch height deviationbecome relatively larger than the influence ratios δ_(wd) and δ_(zd) ofthe groove wall distance deviation (the ratios δ_(w) and δ_(z) of theinfluence ratios become larger) as the groove angle θ becomes large.

For example, when the groove angle θ is 90° (that is, t=1), and thebelow-described adjustment coefficient K_(h) is 1, the ratio δ_(z) ofthe influence ratio of the groove wall distance deviation ΔP_(d) and theinfluence ratio of the torch height deviation ΔP_(h) in the manipulatedvariable Δz of the torch height is represented by “δ_(z)=2(ΔP_(d):ΔP_(h)=1:2), and the ratio δ_(w) of the influence ratio of thegroove wall distance deviation ΔP_(d) and the influence ratio of thetorch height deviation ΔP_(h) in the manipulated variable Δw of theweaving width is represented by “δ_(w)=1 (ΔP_(d):ΔP_(h)=1:1). As anotherexample, when the groove angle θ is 120° (that is, t=1.73), and theadjustment coefficient K_(h) is 1, the influence ratio δ_(z) in themanipulated variable Δz of the torch height is represented by“δ_(z)=3.46 (ΔP_(d):ΔP_(h)=1:3.46), and the influence ratio δ_(w) in themanipulated variable Δw of the weaving width is represented by“δ_(w)=1.73 (ΔP_(d):ΔP_(h)=1:1.73)”. As above, as the groove angle θbecomes large, the influence of the torch height deviation ΔP_(h)becomes larger than the influence of the groove wall distance deviationΔP_(d) in each of the manipulated variables Δz and Δw (the ratios δ_(w)and δ_(z) of the influence ratios become large).

The control unit 22 performs a control operation of driving thehorizontal and vertical actuators 13 and 14 based on the respectivemanipulated variables calculated by the calculation unit 21 to cause thewelding torch 11 to move.

According to the above configuration, each of the manipulated variableΔz of the actuator 14 regarding the torch height and the manipulatedvariable Δw of the actuator 13 regarding the weaving width is calculatedby using both the average arc voltage value of one weaving cycledetected by the sensor 4 and the average arc voltage value of theweaving end portion section detected by the sensor 4. In addition, theinfluence ratios (weight coefficients) by which parameters regarding thegroove wall distance deviation ΔP_(d) and the torch height deviationΔP_(h) in the respective manipulated variables are multiplied are set inaccordance with the groove angle θ of the workpiece 5. Then, byrealizing a setting in which the influence ratio of the torch heightdeviation ΔP_(h) becomes larger than the influence ratio of the groovewall distance deviation ΔP_(d) in each manipulated variable as thegroove angle θ of the workpiece 5 becomes large, the weaving width w andthe torch height z can be quickly, optimally controlled withoutdecreasing the gain. Therefore, by introducing this control model, theweaving width control operation and the torch height control operationcan be simultaneously, sophisticatedly performed.

Each of FIGS. 5A and 5B is a schematic diagram conceptually showing awelding torch control operation of the welding system shown in FIG. 1.FIGS. 5A and 5B are diagrams respectively corresponding to FIGS. 11A and11C showing a conventional example. According to the present embodiment,since the torch height control operation is performed simultaneouslywith the weaving width control operation, the welding torch 11 and theworkpiece 5 can be prevented from abnormally getting close to each otheras shown in FIG. 5A, and the weaving width can be caused to graduallyget close to the target weaving width w_(t) from the initial weavingwidth w₀ within a short control cycle as shown in FIG. 5B.

As shown by Formulas 7 and 8, the manipulated variable is obtained bymultiplying the influence ratio by the adjustment coefficient K_(h) thatadjusts the influence ratio. With this, even if the groove angle θ staysthe same, a more preferable control performance can be realizeddepending on the shape and use of the workpiece 5. The adjustmentcoefficient K_(h) is not indispensable and may be fixed to 1.

The present embodiment has explained the configuration of detecting thearc voltage, but a configuration of detecting the welding current may beused. In this case, since the relation between the current and thedistance becomes opposite to the relation between the voltage and thedistance (as the distance increases, the voltage increases, but thecurrent decreases), a minus (−) sign is added to each formulas ofFormula 6 (that is, Formulas 7 and 8). Moreover, since the arc sensorcontrol operation using the welding current is generally performed in,for example, the MIG welding, the MAG welding, and the CO2 welding, itis preferable that a detected value for the calculation of themanipulated variable be also the welding current value. For example,since the arc sensor control operation using the arc voltage isgenerally performed in the TIG welding, it is preferable that thedetected value for the calculation of the manipulated variable be alsothe arc voltage value.

Example 1

An experiment was carried out, in which the welding system of the aboveembodiment actually performed the TIG welding with respect to theworkpiece. Each of FIGS. 6A and 6B is a diagram showing the shape of theworkpiece used in Example 1. FIG. 6A is a side view, and FIG. 6B is aperspective view. As shown in FIGS. 6A and 6B, the present example hasverified the weld line tracking in a case where as the workpiece 5, aside surface, perpendicular to a short axis, of a steel plate 5A shapedsuch that a plate surface thereof is curved around a short-directionaxis at a longitudinal middle portion thereof was welded to a steelplate 5B inclined at 45° (groove angle θ=90°). In the case of weldingthe workpiece 5 from the left side to the right side in FIG. 6A, a weldline L was such that the welding torch 11 moved to the left in aproceeding direction while it was moving up, and the welding torch 11moved past a middle portion and then moved to the right in theproceeding direction while it was moving down.

Welding conditions of the present example were set as below.

TABLE 1 Items Values Remarks Welding Speed 15 cm/min. Weaving Width 10mm Initial Setting Value Weaving Frequency 2 Hz Weaving Pattern SimpleHarmonic Motion Torch Height of 10 mm Initial Setting Value WeavingCenter Welding Length 300 mm Horizontal Distance in Torch MovingDirection

Then, respective control parameters of Formula 6 in the present examplewere set as below. While performing the weld line tracking, themanipulated variable of the weaving width and the manipulated variableof the torch height were calculated using Formula 6 based on thedetected arc voltage value, and the control operation of the weldingtorch 11 was performed. The arc sensor control operation was notperformed for several seconds from the start until the arc stabilized.Only two points that are a welding start position and a welding endposition were taught to the welding manipulator 1, and the weldingmanipulator 1 was set such that when the control operation was notperformed, the welding torch 11 moves on a straight line connectingthese two points.

TABLE 2 Items Symbols Values Left and Right Gains K_(y) 0.2 mm/VAdjustment Coefficient K_(h) 1 Δz Gain K_(z)   1 mm/V Δw Gain K_(w) 0.2mm/V

Results of actual welding operations performed under the aboveconditions are shown in FIGS. 7A, 7B, 8A, and 8B. FIGS. 7A, 7B, 8A, and8B are diagrams showing results of the arc sensor control operations inExample 1. FIG. 7A is a diagram showing the detected arc voltage. FIG.7B is a diagram showing the deviation of the weaving width from thetarget value. FIG. 8A is a diagram showing the trajectory of thehorizontal position of the welding torch. FIG. 8B is a diagram showingthe trajectory of the vertical position of the welding torch. In FIGS.8A and 8B, the initial value is set to zero.

As shown in FIGS. 8A and 8B, in the present example, both the horizontalposition regarding the weld line tracking and the vertical positionregarding the torch height control operation sophisticatedly tracked thecurved line of the weld line. Especially, due to the shape of theworkpiece 5 of the present example, in the first half of the weldingoperation, since the weld line L extended upward, and the welding torchmoved horizontally, a relative distance between the welding torch 11 andthe workpiece 5 shortened. With this, as shown in FIG. 7B, the weavingwidth was comparatively small. This can also be confirmed by thehorizontal position and weaving amplitude in the first half of FIG. 8A.In contrast, in the second half of the welding operation, since the weldline L extended downward, and the welding torch moved horizontally, therelative distance between the welding torch 11 and the workpiece 5lengthened. With this, as shown in FIG. 7B, the weaving width wascomparatively large. This can also be confirmed by the horizontalposition and weaving amplitude in the second half of FIG. 8A. As above,the present example has shown that the arc welding was being faithfullyperformed in accordance with the shape of the workpiece 5.

Example 2

Further, an experiment was carried out, in which the control mode of thepresent embodiment was compared with Comparative Example. In the presentexample, as with Example 1, the control operation was performed usingFormula 6 based on welding conditions below.

TABLE 3 Items Value Welding Speed 20 cpm Initial Value of Weaving Width8 mm Target Value of Weaving Width 11 mm Weaving Frequency 2 Hz WeavingPattern Simple Harmonic Motion Initial Value of Torch Height of 14 mmWeaving Center Target Value of Torch Height of 10 mm Weaving Center

In Comparative Example, the manipulated variable Δz of the torch heightwas calculated using a formula obtained by removing a term“V_(dref)−(V_(dl)+V_(dr))/2” from the formula of Δz of Formula 6, andthe manipulated variable Δw of the weaving width was calculated using aformula obtained by removing a term “V_(href)−V_(h),” from the formulaof Δw of Formula 6. To be specific, in Comparative Example, the controloperation was performed such that a value of a groove wall distancedirection did not contribute to the calculation of the manipulatedvariable Δz of the torch height, and a value of the torch height did notcontribute to the calculation of the manipulated variable Δw of theweaving width. For facilitating the comparison, the values of respectivegains were set to be different between the present example andComparative Example. The arc sensor control operation was not performedfor several seconds from the start until the arc stabilized.

Results of actual welding operations performed under the aboveconditions are shown in FIGS. 9A, 9B, 10A, and 10B. FIGS. 9A, 9B, 10A,and 10B are diagrams showing results of the arc sensor controloperations in Example 2 and Comparative Example. FIG. 9A is a diagramshowing a time change of the weaving width. FIG. 9B is a diagram showinga time change of the horizontal distance between the weaving end and theworkpiece. FIG. 10A is a diagram showing a time change of the torchheight of the weaving center. FIG. 10B is a diagram showing a timechange of the average torch height.

As shown in FIG. 9A, in Comparative Example, the weaving width overshotimmediately after the start of the control operation. To be specific, asshown in FIG. 9B, the horizontal distance between the welding torch 11and the workpiece 5 abnormally got close to each other. This abnormalcloseness becomes a cause of the weld defect, such as undercut. Incontrast, in the present example, the weaving width control operationwas smoothly performed without causing the overshoot, there was no fearof the weld defect unlike Comparative Example, and the weaving width wasstable after a predetermined period of time. Regarding the torch height,as shown in FIGS. 10A and 10B, the torch height overshot immediatelyafter the start of the control operation in Comparative Example whereasthe torch height was smoothly, stably controlled in the present example.As is clear from the above, by using the control method of the presentembodiment, each of the weaving width and the torch height can quicklybecome the target value without causing the overshoot.

From the foregoing explanation, many modifications and other embodimentsof the present invention are obvious to one skilled in the art.Therefore, the foregoing explanation should be interpreted only as anexample and is provided for the purpose of teaching the best mode forcarrying out the present invention to one skilled in the art. Thestructures and/or functional details may be substantially modifiedwithin the spirit of the present invention.

The embodiment of the present invention has been explained as above.However, the present invention is not limited to the above embodiment.Various improvements, changes, and modifications may be made within thespirit of the present invention.

INDUSTRIAL APPLICABILITY

The arc welding control system and method of the present invention areuseful for simultaneously, sophisticatedly performing the weaving widthcontrol operation and the torch height control operation.

REFERENCE SIGNS LIST

-   -   1 welding manipulator    -   2 calculation control unit    -   3 welding power source    -   4 sensor    -   5 workpiece    -   11 welding torch    -   12 electrode    -   13 horizontal actuator    -   14 vertical actuator    -   21 calculation unit    -   22 control unit    -   41 voltage sensor    -   42 current sensor    -   51 groove    -   θ groove angle

The invention claimed is:
 1. An arc sensor control system for arcwelding for obtaining satisfactory beads in a groove of a workpiece thatis a welding target, the arc sensor control system comprising: anactuator configured to cause a welding torch to track a weld line of theworkpiece by causing the welding torch to move in a direction of theweld line of the workpiece at a specified torch height while causing thewelding torch to move in a cyclic manner in a width direction of thegroove of the workpiece with a specified weaving width; a sensorconfigured to detect a welding current or an arc voltage; a calculationunit configured to obtain from the welding current or the arc voltage avalue corresponding to a groove wall distance indicating a horizontaldistance between the welding torch and the workpiece at a weaving endportion and a value corresponding to the torch height, calculate adifference between the value corresponding to the groove wall distanceand a target value and a difference between the value corresponding tothe torch height and a target value, calculate a manipulated variable ofthe actuator regarding the weaving width using a groove wall distancedeviation that is a deviation of the value corresponding to the groovewall distance from the target value, a torch height deviation that is adeviation of the value corresponding to the torch height from the targetvalue, and a first ratio that is a ratio of a degree of influence of thetorch height deviation on the manipulated variable of the actuatorregarding the weaving width to a degree of influence of the groove walldistance deviation on the manipulated variable of the actuator regardingthe weaving width, and calculate a manipulated variable of the actuatorregarding the torch height using the groove wall distance deviation, thetorch height deviation, and a second ratio that is a ratio of a degreeof influence of the torch height deviation on the manipulated variableof the actuator regarding the torch height to a degree of influence ofthe groove wall distance deviation on the manipulated variable of theactuator regarding the torch height; and a control unit configured tocontrol the weaving width and the torch height based on the manipulatedvariable regarding the weaving width and the manipulated variableregarding the torch height, wherein: each of the first and second ratiosis set so as to increase as the groove angle increases.
 2. The arcsensor control system according to claim 1, wherein the manipulatedvariable of the actuator regarding the weaving width is obtained bymultiplying the first ratio by an adjustment coefficient for adjustingthe first ratio, and the manipulated variable of the actuator regardingthe torch height is obtained by multiplying the second ratio by anadjustment coefficient for adjusting the second ratio.
 3. The arc sensorcontrol system according to claim 1, wherein the calculation unit isconfigured to: calculate an average value of the welding current or arcvoltage for each of a plurality of sections of one weaving cycle, thewelding current or arc voltage being detected by the sensor, theplurality of sections being obtained by dividing one weaving cycle intoa predetermined number; obtain the value corresponding to the groovewall distance based on the average value of one or a plurality ofsections corresponding to the weaving end portion among the plurality ofsections; and obtain the value corresponding to the torch height basedon the average value of the welding current or arc voltage of oneweaving cycle.
 4. The arc sensor control system according to claim 2,wherein: a manipulated variable Δz of the torch height is represented byFormula 1 below; and a manipulated variable Δw of the weaving width isrepresented by Formula 2 below, $\begin{matrix}{{\Delta\; z} = {K_{z}\left( {{- \frac{\Delta\; P_{d}}{t}} + {2\; K_{h}\Delta\; P_{h}}} \right)}} & {{Formula}\mspace{14mu} 1} \\{{\Delta\; w} = {4\;{K_{w}\left( {{{- \Delta}\; P_{d}} + {{tK}_{h}\Delta\; P_{h}}} \right)}}} & {{Formula}\mspace{14mu} 2}\end{matrix}$ where K_(z) denotes a gain of the manipulated variableregarding the torch height, K_(w) denotes a gain of the manipulatedvariable regarding the weaving width, ΔP_(d) denotes the groove walldistance deviation, ΔP_(h) denotes the torch height deviation, t denotesa value represented by “t=tan(θ/2)” where θ denotes the groove angle,and K_(h) denotes the adjustment coefficient.